These and other developments have some reproductive health experts wondering if opposition to embryonic stem cell research may broaden to include in vitro fertilization, a mainstream medical procedure used by millions of people.

Abortion opponents contacted by the Chicago Tribune said they were not aware of any lobbying to ban or restrict IVF - but they'd happily support such legislation.

"IVF requires killing," said Bill Beckman, executive director of the Illinois Right to Life Committee. "They choose which (embryos) to implant, and they create spares that will die."

The cells used in embryonic stem cell research come from IVF embryos, which critics believe deserve the same ethical treatment as living children. The debate has raised awareness that this procedure typically creates more embryos than are used to make babies.

Many experts believe IVF is now far too commonplace to be drastically restricted. The American Society for Reproductive Medicine estimates that one of every 100 children born in the U.S. is conceived this way.

Beckman agreed that trying to limit IVF would be difficult, adding that abortion and euthanasia are higher priorities. "There are too many battles to fight, and IVF is not at the top of the priority list," he said.

"It doesn't have the same priority for us as stem cell research," agreed Carrie Gordon Earll of Focus on the Family. "There are only so many man-hours to go around."

Yet a variety of recent events are provoking anxiety in the field of assisted reproduction.

In Kentucky, draft legislation would force IVF practitioners to fertilize only one egg at a time. The usual practice is to fertilize multiple eggs and preserve some in case the woman doesn't get pregnant on the first try.

If the Kentucky bill passed, it "would dramatically lower pregnancy rates," said Dr. Richard Scott, director of Reproductive Medicine Associates on the East Coast. "Tens of thousands of people a year will go without a family."

President Bush and other politicians, meanwhile, are promoting "embryo adoption" as an alternative to destroying leftover embryos. A spokesman for Americans United for Life said his group is researching model legislation for states that want to regulate reproductive technologies. Already, Louisiana bans the intentional destruction of a viable fertilized egg.

At the individual level, IVF raises complicated moral issues. Many patients who describe themselves as "pro-life" have no compunction about creating new life through the procedure, experts agreed. On the other hand, some "pro-choice" people find they can't destroy or donate their leftover embryos.

In IVF, a woman is given hormones so her ovaries will produce a large number of eggs at once. The eggs are removed and fertilized in a lab. After the fertilized eggs start dividing, one or more embryos are transferred to the woman's uterus in hopes that one will implant and develop into a fetus.

Remaining healthy embryos are usually saved for future pregnancy attempts. Frozen embryos have been accumulating since the late 1970s, creating a stockpile estimated at more than 400,000.

Those embryos are a potential source of stem cells, which researchers believe might be able to generate replacement tissues that could help people with cancer, diabetes and other diseases.

Whether doing that is morally acceptable hinges on the question of when life begins - the same question at the root of the abortion debate.

To those who believe a human life is created the moment egg meets sperm, abortion is murder. So is destroying a frozen embryo.

But Beckman estimates fewer than 10 percent of Americans hold that view. Many who oppose abortion are in favor of IVF and embryonic stem cell research. And some who oppose stem cell research, such as Bush, support IVF.

"Being anti-abortion isn't necessarily going to make you (anti-IVF)," said Eleanor Nicoll of the society for reproductive medicine. "Many people are capable of making distinctions between removal of a fetus from the uterus and an embryo in a dish."

The feelings involved can be complex. Kristin Daus, a church-going Catholic, had two children through assisted reproduction and a third the old-fashioned way.

Daus, 38, knows she violated church teaching by going through IVF. She strongly supports stem cell research, and she believes abortion should be legal for those who choose it.

But once she was done having children, she said, she felt morally obligated to the six frozen embryos she and her husband, Jerry, had left behind.